Field of the Invention
The present invention relates to a magnetic carrier used in an image forming method including the step of developing (visualizing) an electrostatic latent image (static charge image) using an electrophotographic method.
Description of the Related Art
Conventionally, for an electrophotographic image forming method, a method including forming an electrostatic latent image on an electrostatic latent image bearing member using various units, and adhering a toner to the electrostatic latent image to develop the electrostatic latent image is generally used. In the development, a two-component development system is widely adopted. In this system, a support particle referred to as a magnetic carrier is mixed with a toner, the mixture is subjected to triboelectric charging to provide an appropriate amount of a positive or negative charge to the toner, and development is performed using the charge as driving force.
In the two-component development system, functions such as the stirring, conveyance, and charging of the developer can be provided to the magnetic carrier, and therefore function assignments of the magnetic carrier and the toner are clear. Thus, the two-component development system has advantages such as good controlling properties of developer performance.
On the other hand, in recent years, due to technical evolution in the electrophotographic field, higher speed and longer life of the apparatus as well as higher definition and the stabilization of image quality have been increasingly severely required. For example, the requirements include maintaining moderate charging properties of the toner particle over a long period, impact resistance, and wear resistance as well as stably maintaining the charging properties of the toner particle against a change in an environment such as humidity or temperature.
In order to satisfy these requirements, various researches and the like have been performed, and various resin covering carriers have been proposed.
In such circumstances, Japanese Patent Application Laid-Open No. 2004-233905, Japanese Patent Application Laid-Open No. 2009-145845, Japanese Patent Application Laid-Open No. 2006-267297, Japanese Patent Application Laid-Open No. 2001-194832, Japanese Patent Application Laid-Open No. 2000-098666, and Japanese Patent Application Laid-Open No. 2012-252332 describe techniques of containing inorganic fine particles in covering resins. Fog, toner scattering, charge maintaining properties, carrier contamination, and environmental stability are improved by these magnetic carriers. But there is still room for improvement regarding environmental stability, particularly image quality stability during environmental change, and further development and study is necessary.